Lower molecular weight alcohols and ethers such as isopropanol (IPA) and diisopropyl ether (DIPE) are in the gasoline boiling range and are known to have high blending octane numbers. In addition, by-product propylene from which IPA and DIPE can be made is usually available in a fuels refinery. An important aspect of research in the petroleum industry relates to processes to produce high octane lower aliphatic alkyl ethers as octane boosters and supplementary fuels.
The catalytic hydration of olefins, particularly C.sub.3 and C.sub.4 olefins, to provide alcohols and ethers is a well-established art and is of significant commercial importance. Representative olefin hydration processes are disclosed in U.S. Pat. Nos. 2,262,913;2,477,380; 2,797,247; 3,798,097; 2,805,260; 2,830,090; 2,861,045; 2,891,999; 3,006,970; 3,198,752; 3,810,848; 3,989,762, among others.
The production of ether from secondary alcohols such as isopropanol and light olefins is known. As disclosed in U.S. Pat. No. 4,182,914, DIPE is produced from IPA and propylene in a series of operations employing a strongly acidic cation exchange resin as catalyst. Recently, processes for the hydration of olefins to provide alcohols and ethers using zeolite catalyst have been disclosed by Bell et al. in U.S. patent applications Ser. Nos. 414,630 filed Sept. 26, 1989; 427,926 filed Oct. 25, 1989; and U.S. Pat. Nos. 4,214,107 and 4,499,313 to Bell et al.; and U.S. Pat. No. 4,757,664 and 4,906,187 to T. Huang. These applications and patents are incorporated herein in their entirety by reference.
In the conversion of a water feedstream and a C.sub.3 hydrocarbons feedstream comprising propene and propane to DIPE and IPA as conventionally practiced, the conversion per pass is about 60%. The reaction effluent is a mixture containing unreacted water, C.sub.3 hydrocarbons and hydrocarbon oligomeric by-products, in addition to the DIPE and IPA products. Separating these components requires multiple distillation and extraction operations that represent a substantial part of the overall process costs. C.sub.3 and any lower hydrocarbons present are effectively removed by distillation. However, separation of DIPE and IPA is accomplished by an aqueous extraction operation that requires a further distillation step to separate alcohol and water. This extraction and distillation of IPA from the reaction effluent in order to recycle IPA to the etherification reactor as typically carried out imposes an inordinate cost burden on the process in view of the formation of an IPA-water azeotrope which affects the complexity of the distillation tower design and operation.
It is an object of the present invention to provide a process for the production of diisopropyl ether at lower overall process cost and complexity.
It is another object of the present invention to provide an improved process for the steps of product separation and recycle of IPA in downstream DIPE operations.
Another object of the present invention is to utilize the DIPE water feed as at least a portion of the water used to wash the DIPE reactor effluent.
A further object of the invention is to provide an improved distillation step in the separation of aqueous isopropanol in the DIPE process.